ApiDemos学习知识点之media-AudioFx（9）

本demo主要针对于声音波形播放的演示。

本demo中应用了很多知识点，在后面一一进行介绍和解读，现在先上一下本demo的运行界面。

接下来看一下简单的波形控件自定义类

class VisualizerView extends View {    private byte[] mBytes;    private float[] mPoints;    private Rect mRect = new Rect();    private Paint mForePaint = new Paint();    public VisualizerView(Context context) {        super(context);        init();    }    private void init() {        mBytes = null;        mForePaint.setStrokeWidth(1f);        mForePaint.setAntiAlias(true);        mForePaint.setColor(Color.rgb(0, 128, 255));    }    public void updateVisualizer(byte[] bytes) {        mBytes = bytes;        invalidate();    }    @Override    protected void onDraw(Canvas canvas) {        super.onDraw(canvas);        if (mBytes == null) {            return;        }        if (mPoints == null || mPoints.length < mBytes.length * 4) {            mPoints = new float[mBytes.length * 4];        }        mRect.set(0, 0, getWidth(), getHeight());        for (int i = 0; i < mBytes.length - 1; i++) {            mPoints[i * 4] = mRect.width() * i / (mBytes.length - 1);            mPoints[i * 4 + 1] = mRect.height() / 2                    + ((byte) (mBytes[i] + 128)) * (mRect.height() / 2) / 128;            mPoints[i * 4 + 2] = mRect.width() * (i + 1) / (mBytes.length - 1);            mPoints[i * 4 + 3] = mRect.height() / 2                    + ((byte) (mBytes[i + 1] + 128)) * (mRect.height() / 2) / 128;        }        canvas.drawLines(mPoints, mForePaint);    }}

自定义控件的知识，就不在此处赘述了，有兴趣的小伙伴可以翻阅之前的自定义控件章节。

接下来看下运行时的Activity

做频谱应用到了Visualizer 类，这个类只在Android 2.3以上的API才支持

public class AudioFxDemo extends Activity {    private static final String TAG = "AudioFxDemo";    private static final float VISUALIZER_HEIGHT_DIP = 50f;    private MediaPlayer mMediaPlayer;    private Visualizer mVisualizer;    private Equalizer mEqualizer;    private LinearLayout mLinearLayout;    private VisualizerView mVisualizerView;    private TextView mStatusTextView;    @Override    public void onCreate(Bundle icicle) {        super.onCreate(icicle);        setVolumeControlStream(AudioManager.STREAM_MUSIC);        mStatusTextView = new TextView(this);        mLinearLayout = new LinearLayout(this);        mLinearLayout.setOrientation(LinearLayout.VERTICAL);        mLinearLayout.addView(mStatusTextView);        setContentView(mLinearLayout);        //创建媒体播放器Create the MediaPlayer        mMediaPlayer = MediaPlayer.create(this, R.raw.test_cbr);        / /创建一个VisualizerView(自定义)，它将呈现简化的音频波浪形式到画布。        setupVisualizerFxAndUI();        setupEqualizerFxAndUI();        // Make sure the visualizer is enabled only when you actually want to receive data, and        // when it makes sense to receive data.        mVisualizer.setEnabled(true);        // When the stream ends, we don't need to collect any more data. We don't do this in        // setupVisualizerFxAndUI because we likely want to have more, non-Visualizer related code        // in this callback.        mMediaPlayer.setOnCompletionListener(new MediaPlayer.OnCompletionListener() {            public void onCompletion(MediaPlayer mediaPlayer) {                mVisualizer.setEnabled(false);            }        });        mMediaPlayer.start();        mStatusTextView.setText("Playing audio...");    }    private void setupEqualizerFxAndUI() {        / /创建均衡器对象(一个AudioEffect子类)并将其附加到我们的媒体播放器上， 具有默认优先级(0)。        mEqualizer = new Equalizer(0, mMediaPlayer.getAudioSessionId());        mEqualizer.setEnabled(true);        TextView eqTextView = new TextView(this);        eqTextView.setText("Equalizer:");        mLinearLayout.addView(eqTextView);        short bands = mEqualizer.getNumberOfBands();        final short minEQLevel = mEqualizer.getBandLevelRange()[0];        final short maxEQLevel = mEqualizer.getBandLevelRange()[1];        for (short i = 0; i < bands; i++) {            final short band = i;            TextView freqTextView = new TextView(this);            freqTextView.setLayoutParams(new ViewGroup.LayoutParams(                    ViewGroup.LayoutParams.FILL_PARENT,                    ViewGroup.LayoutParams.WRAP_CONTENT));            freqTextView.setGravity(Gravity.CENTER_HORIZONTAL);            freqTextView.setText((mEqualizer.getCenterFreq(band) / 1000) + " Hz");            mLinearLayout.addView(freqTextView);            LinearLayout row = new LinearLayout(this);            row.setOrientation(LinearLayout.HORIZONTAL);            TextView minDbTextView = new TextView(this);            minDbTextView.setLayoutParams(new ViewGroup.LayoutParams(                    ViewGroup.LayoutParams.WRAP_CONTENT,                    ViewGroup.LayoutParams.WRAP_CONTENT));            minDbTextView.setText((minEQLevel / 100) + " dB");            TextView maxDbTextView = new TextView(this);            maxDbTextView.setLayoutParams(new ViewGroup.LayoutParams(                    ViewGroup.LayoutParams.WRAP_CONTENT,                    ViewGroup.LayoutParams.WRAP_CONTENT));            maxDbTextView.setText((maxEQLevel / 100) + " dB");            LinearLayout.LayoutParams layoutParams = new LinearLayout.LayoutParams(                    ViewGroup.LayoutParams.FILL_PARENT,                    ViewGroup.LayoutParams.WRAP_CONTENT);            layoutParams.weight = 1;            SeekBar bar = new SeekBar(this);            bar.setLayoutParams(layoutParams);            bar.setMax(maxEQLevel - minEQLevel);            bar.setProgress(mEqualizer.getBandLevel(band));            bar.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {                public void onProgressChanged(SeekBar seekBar, int progress,                        boolean fromUser) {                    mEqualizer.setBandLevel(band, (short) (progress + minEQLevel));                }                public void onStartTrackingTouch(SeekBar seekBar) {}                public void onStopTrackingTouch(SeekBar seekBar) {}            });            row.addView(minDbTextView);            row.addView(bar);            row.addView(maxDbTextView);            mLinearLayout.addView(row);        }    }    private void setupVisualizerFxAndUI() {        // Create a VisualizerView (defined below), which will render the simplified audio        // wave form to a Canvas.        mVisualizerView = new VisualizerView(this);        mVisualizerView.setLayoutParams(new ViewGroup.LayoutParams(                ViewGroup.LayoutParams.FILL_PARENT,                (int)(VISUALIZER_HEIGHT_DIP * getResources().getDisplayMetrics().density)));        mLinearLayout.addView(mVisualizerView);        // 首先实例化Visualizer，参数SessionId可以通过MediaPlayer的对象获得        mVisualizer = new Visualizer(mMediaPlayer.getAudioSessionId());

//接着设置需要转换的音乐内容长度，专业的说这就是采样，该采样值一般为2的指数倍，如64,128,256,512,1024        mVisualizer.setCaptureSize(Visualizer.getCaptureSizeRange()[1]);

//为visualizer设置监听器，当Capture一段数据后，就会触发两个函数进行处理samplingRate是采样速率，即rate值，512mHz。其中两个byte[] waveform和byte[] fft数组，分别是获得波形数据和FFT的数据，该byte数组的大小即为之前设置的采样值大小128，获得数据如下图所示。其中n为采样值，index 0 表示直流分量，Rf表示FFT计算后的实部，If表示FFT计算后的虚部。        mVisualizer.setDataCaptureListener(new Visualizer.OnDataCaptureListener() {            public void onWaveFormDataCapture(Visualizer visualizer, byte[] bytes,                    int samplingRate) {                mVisualizerView.updateVisualizer(bytes);            }            public void onFftDataCapture(Visualizer visualizer, byte[] bytes, int samplingRate) {}        }, Visualizer.getMaxCaptureRate() / 2, true, false);    }//暂停播放器    @Override    protected void onPause() {        super.onPause();        if (isFinishing() && mMediaPlayer != null) {            mVisualizer.release();            mEqualizer.release();            mMediaPlayer.release();            mMediaPlayer = null;        }    }}